1. Field
This invention generally relates to wireless communications and, more specifically, to channel interleaving for communication systems providing broadcast/multicast services.
2. Background
The field of wireless communications has many applications including, e.g., cordless telephones, paging, wireless local loops, personal digital assistants (PDAs), Internet telephony, and satellite communication systems. A particularly important application is cellular telephone systems for mobile subscribers. As used herein, the term “cellular” system encompasses both cellular and personal communications services (PCS) frequencies. Various over-the-air interfaces have been developed for such cellular telephone systems including, e.g., Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiplexing (OFDM) modulation, Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). In connection therewith, various domestic and international standards have been established including, e.g., Advanced Mobile Phone Service (AMPS), Global System for Mobile (GSM), and Interim Standard 95 (IS-95). In particular, IS-95 and its derivatives, IS-95A, IS-95B, ANSI J-STD-008 (often referred to collectively herein as IS-95), and proposed high data rate systems for data, etc., are promulgated by the Telecommunication Industry Association (TIA), the International Telecommunications Union (ITU), and other well known standards bodies.
Cellular telephone systems configured in accordance with the use of the IS-95 standard employ CDMA signal processing techniques to provide highly efficient and robust cellular telephone service. Exemplary cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. Pat. Nos. 5,103,459 and 4,901,307. An exemplary system utilizing CDMA techniques is the cdma2000. The standard for cdma2000 is given in Standard IS-2000, which is compatible with IS-95 systems in many ways. Another CDMA standard is the WCDMA standard, as embodied in 3rd Generation Partnership Project “3GPP”, Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214. Another CDMA standard is Standard IS-856, which is commonly referred to as a High Data Rate (HDR) system.
Transmission of digital data is inherently prone to interference, which may introduce errors into the transmitted data. To improve the performance of a transmission channel, some coding schemes include interleavers, which mix up the order of the bits in the packet during coding. Thus, when interference destroys some adjacent bits during transmission, the effect of the interference is spread out over the entire original packet and can more readily be overcome by the decoding process. Recently, broadcast/multicast services have been proposed to effectively transmit large quantities of data from a single source point to a group of users in wireless communication systems. Contents suitable for such point-to-multipoint services include news, stock quotes, sports events, movies, audio and video clips, and other multimedia data. As the demand for transmission of multimedia data grows, there lies a challenge to enhance such services and a need for enhanced channel interleaving supporting broadcast/multicast services.